A leak detector for evaporated fuel detects leakage of the evaporated fuel generated in a fuel tank. This detector is disclosed in, for example, US Patent Application Publication No. 2004/0000187-A1. In this detector, the evaporated fuel is adsorbed to adsorbent such as granular activated carbon in an adsorption chamber. The adsorbed evaporated fuel is discharged to an intake pipe side by negative pressure in an evaporated fuel processing system. The detector detects leakage of the evaporated fuel processing system.
The pressure in the evaporated fuel processing system disposed on a fuel tank side is pressurized or depressurized by a pump so that the leakage of the evaporated fuel is detected. A passage among an atmosphere side, the fuel tank side and a pump side is switched in accordance with operation and stop of the pump by an electromagnetic valve.
However, the leakage detection of the evaporated fuel is performed when the engine of an automotive vehicle is stopped. In this case, electricity is not supplied from a generator to a battery in the vehicle. Therefore, the leakage detection is not sufficiently performed when sufficient electricity is not supplied to the electromagnetic valve since the battery is deteriorated or the electricity supply performance of the battery is reduced in case of low temperature. Further, since the electromagnetic valve is composed of a core, a coil and the like, the weight and dimensions of the leak detector become larger. Thus, it is required to reduce electricity consumption of the leak detector and to reduce the weight and the dimensions of the leak detector.